The role of AMPA receptors in postsynaptic mechanisms of synaptic plasticity

Plasticity-induced actin polymerization in the dendritic shaft regulates intracellular AMPA receptor trafficking

AMPA-type receptors (AMPARs) are rapidly inserted into synapses undergoing plasticity to increase synaptic transmission, but it is not fully understood if and how AMPAR-containing vesicles are selectively trafficked to these synapses. Here, we developed a strategy to label AMPAR GluA1 subunits expressed from their endogenous loci in cultured rat hippocampal neurons and characterized the motion of GluA1-containing vesicles using single-particle tracking and mathematical modeling. We find that GluA1-containing vesicles are confined and concentrated near sites of stimulation-induced structural plasticity. We show that confinement is mediated by actin polymerization, which hinders the active transport of GluA1-containing vesicles along the length of the dendritic shaft by modulating the rheological properties of the cytoplasm. Actin polymerization also facilitates myosin-mediated transport of GluA1-containing vesicles to exocytic sites. We conclude that neurons utilize F-actin to increase vesicular GluA1 reservoirs and promote exocytosis proximal to the sites of synaptic activity.

Mechanisms of neurodevelopmental toxicity of topiramate

Prescriptions for antiseizure medications (ASMs) have been rapidly growing over the last several decades due, in part, to an expanding list of clinical indications for which they are now prescribed. This trend has raised concern for potential adverse neurodevelopmental outcomes in ASM-exposed pregnancies. Recent large scale population studies have suggested that the use of topiramate (TOPAMAX, Janssen-Cilag), when prescribed for seizure control, migraines, and/or weight management, is associated with an increased risk for autism spectrum disorder (ASD), intellectual disability, and attention-deficit/hyperactivity disorder (ADHD) in exposed offspring. Here, we critically review epidemiologic evidence demonstrating the neurobehavioral teratogenicity of topiramate and speculate on the neuromolecular mechanisms by which prenatal exposure may perturb neurocognitive development. Specifically, we explore the potential role of topiramate's pharmacological interactions with ligand- and voltage-gated ion channels, especially GABAergic signaling, its effects on DNA methylation and histone acetylation, whether topiramate induces oxidative stress, and its association with fetal growth restriction as possible mechanisms contributing to neurodevelopmental toxicity. Resolving this biology will be necessary to reduce the risk of adverse pregnancy outcomes caused by topiramate or other ASMs.

Tau-mediated synaptic dysfunction is coupled with HCN channelopathy

INTRODUCTION

In tauopathies, altered tau processing correlates with impairments in synaptic density and function. Changes in hyperpolarization-activated cyclic nucleotide-gated (HCN) channels contribute to disease-associated abnormalities in multiple neurodegenerative diseases.

METHODS

To investigate the link between tau and HCN channels, we performed histological, biochemical, ultrastructural, and functional analyses of hippocampal tissues from Alzheimer's disease (AD), age-matched controls, Tau35 mice, and/or Tau35 primary hippocampal neurons.

RESULTS

Expression of specific HCN channels is elevated in post mortem AD hippocampus. Tau35 mice develop progressive abnormalities including increased phosphorylated tau, enhanced HCN channel expression, decreased dendritic branching, reduced synapse density, and vesicle clustering defects. Tau35 primary neurons show increased HCN channel expression enhanced hyperpolarization-induced membrane voltage "sag" and changes in the frequency and kinetics of spontaneous excitatory postsynaptic currents.

DISCUSSION

Our findings are consistent with a model in which pathological changes in tauopathies impact HCN channels to drive network-wide structural and functional synaptic deficits.

HIGHLIGHTS

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are functionally linked to the development of tauopathy. Expression of specific HCN channels is elevated in the hippocampus in Alzheimer's disease and the Tau35 mouse model of tauopathy. Increased expression of HCN channels in Tau35 mice is accompanied by hyperpolarization-induced membrane voltage "sag" demonstrating a detrimental effect of tau abnormalities on HCN channel function. Tau35 expression alters synaptic organization, causing a loosened vesicle clustering phenotype in Tau35 mice.

The Chemokine CCL2 Promotes Excitatory Synaptic Transmission in Hippocampal Neurons via GluA1 Subunit Trafficking

The CC chemokine ligand 2 (CCL2, also known as MCP-1) and its cognate receptor CCR2 have well-characterized roles in chemotaxis. CCL2 has been previously shown to promote excitatory synaptic transmission and neuronal excitability. However, the detailed molecular mechanism underlying this process remains largely unclear. In cultured hippocampal neurons, CCL2 application rapidly upregulated surface expression of GluA1, in a CCR2-dependent manner, assayed using SEP-GluA1 live imaging, surface GluA1 antibody staining, and electrophysiology. Using pharmacology and reporter assays, we further showed that CCL2 upregulated surface GluA1 expression primarily via Gαq- and CaMKII-dependent signaling. Consistently, using i.p. injection of lipopolysaccharide to induce neuroinflammation, we found upregulated phosphorylation of S831 and S845 sites on AMPA receptor subunit GluA1 in the hippocampus, an effect blocked in Ccr2-/- mice. Together, these results provide a mechanism through which CCL2, and other secreted molecules that signal through G-protein coupled receptors, can directly regulate synaptic transmission.

A discrete subpopulation of PFC-LHb neurons govern cocaine place preference

Addiction is a complex behavioral disorder characterized by compulsive drug-seeking and drug use despite harmful consequences. The prefrontal cortex (PFC) plays a crucial role in cocaine addiction, involving decision-making, impulse control, memory, and emotional regulation. The PFC interacts with the brain's reward system, including the ventral tegmental area (VTA) and nucleus accumbens (NAc). The PFC also projects to the lateral habenula (LHb), a brain region critical for encoding negative reward and regulating the reward system. In the current study, we examined the role of PFC-LHb projections in regulating cocaine reward-related behaviors. We found that optogenetic stimulation of the PFC-LHb circuit during cocaine conditioning abolished cocaine preference without causing aversion. In addition, increased c-fos expression in LHb neurons was observed in animals that received optic stimulation during cocaine conditioning, supporting the circuit's involvement in cocaine preference regulation. Molecular analysis in animals that received optic stimulation revealed that cocaine-induced alterations in the expression of GluA1 subunit of AMPA receptor was normalized to saline levels in a region-specific manner. Moreover, GluA1 serine phosphorylation on S845 and S831 were differentially altered in LHb and VTA but not in the PFC. Together these findings highlight the critical role of the PFC-LHb circuit in controlling cocaine reward-related behaviors and shed light on the underlying mechanisms. Understanding this circuit's function may provide valuable insights into addiction and contribute to developing targeted treatments for substance use disorders.

HDAC1/2/3-mediated downregulation of neurogranin is involved in cognitive impairment in offspring exposed to maternal subclinical hypothyroidism

Subclinical hypothyroidism (SCH) in pregnancy is the most common form of thyroid dysfunction in pregnancy, which can affect fetal nervous system development and increase the risk of neurodevelopmental disorders after birth. However, the mechanism of the effect of maternal subclinical hypothyroidism on fetal brain development and behavioral phenotypes is still unclear and requires further study. In this study, we constructed a mouse model of maternal subclinical hypothyroidism by exposing dams to drinking water containing 50 ppm propylthiouracil (PTU) during pregnancy and found that its offspring were accompanied by severe cognitive deficits by behavioral testing. Mechanistically, gestational SCH resulted in the upregulation of protein expression and activity of HDAC1/2/3 in the hippocampus of the offspring. ChIP analysis revealed that H3K9ac on the neurogranin (Ng) promoter was reduced in the hippocampus of the offspring of SCH, with a significant reduction in Ng protein, leading to reduced expression levels of synaptic plasticity markers PSD95 (a membrane-associated protein in the postsynaptic density) and SYN (synaptophysin, a specific marker for presynaptic terminals), and impaired synaptic plasticity. In addition, administration of MS-275 (an HDAC1/2/3-specific inhibitor) to SCH offspring alleviated impaired synaptic plasticity and cognitive dysfunction in offspring. Thus, our study suggests that maternal subclinical hypothyroidism may mediate offspring cognitive dysfunction through the HDAC1/2/3-H3K9ac-Ng pathway. Our study contributes to the understanding of the signaling mechanisms underlying maternal subclinical hypothyroidism-mediated cognitive impairment in the offspring.

Extracellular ATP inhibits excitatory synaptic input on parvalbumin positive interneurons and attenuates gamma oscillations via P2X4 receptors

BACKGROUND AND PURPOSE

P2X4 receptors (P2X4R) are ligand gated cation channels that are activated by extracellular ATP released by neurons and glia. The receptors are widely expressed in the brain and have fractional calcium currents comparable with NMDA receptors. Although P2X4Rs have been reported to modulate synaptic transmission and plasticity, their involvement in shaping neuronal network activity remains to be elucidated.

EXPERIMENTAL APPROACH

We investigated the effects of P2X receptors at network and synaptic level using local field potential electrophysiology, whole cell patch clamp recordings and calcium imaging in fast spiking parvalbumin positive interneurons (PVINs) in rat and mouse hippocampal slices. The stable ATP analogue ATPγS, selective antagonists and P2X4R knockout mice were used.

KEY RESULTS

The P2XR agonist ATPγS reversibly decreased the power of gamma oscillations. This inhibition could be antagonized by the selective P2X4R antagonist PSB-12062 and was not observed in P2X4-/- mice. The phasic excitatory inputs of CA3 PVINs were one of the main regulators of the gamma power. Associational fibre compound excitatory postsynaptic currents (cEPSCs) in CA3 PVINs were inhibited by P2X4R activation. This effect was reversible, dependent on intracellular calcium and dynamin-dependent internalization of AMPA receptors.

CONCLUSIONS AND IMPLICATIONS

The results indicate that P2X4Rs are an important source of dendritic calcium in CA3 PVINs, thereby regulating excitatory synaptic inputs onto the cells and presumably the state of gamma oscillations in the hippocampus. P2X4Rs represent an effective target to modulate hippocampal network activity in pathophysiological conditions such as Alzheimer's disease and schizophrenia.

Synaptic homeostasis transiently leverages Hebbian mechanisms for a multiphasic response to inactivity

Homeostatic regulation of synapses is vital for nervous system function and key to understanding a range of neurological conditions. Synaptic homeostasis is proposed to operate over hours to counteract the destabilizing influence of long-term potentiation (LTP) and long-term depression (LTD). The prevailing view holds that synaptic scaling is a slow first-order process that regulates postsynaptic glutamate receptors and fundamentally differs from LTP or LTD. Surprisingly, we find that the dynamics of scaling induced by neuronal inactivity are not exponential or monotonic, and the mechanism requires calcineurin and CaMKII, molecules dominant in LTD and LTP. Our quantitative model of these enzymes reconstructs the unexpected dynamics of homeostatic scaling and reveals how synapses can efficiently safeguard future capacity for synaptic plasticity. This mechanism of synaptic adaptation supports a broader set of homeostatic changes, including action potential autoregulation, and invites further inquiry into how such a mechanism varies in health and disease.

Novel α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor (AMPAR) potentiator LT-102: A promising therapeutic agent for treating cognitive impairment associated with schizophrenia

AIMS

We aimed to evaluate the potential of a novel selective α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor (AMPAR) potentiator, LT-102, in treating cognitive impairments associated with schizophrenia (CIAS) and elucidating its mechanism of action.

METHODS

The activity of LT-102 was examined by Ca2+ influx assays and patch-clamp in rat primary hippocampal neurons. The structure of the complex was determined by X-ray crystallography. The selectivity of LT-102 was evaluated by hERG tail current recording and kinase-inhibition assays. The electrophysiological characterization of LT-102 was characterized by patch-clamp recording in mouse hippocampal slices. The expression and phosphorylation levels of proteins were examined by Western blotting. Cognitive function was assessed using the Morris water maze and novel object recognition tests.

RESULTS

LT-102 is a novel and selective AMPAR potentiator with little agonistic effect, which binds to the allosteric site formed by the intradimer interface of AMPAR's GluA2 subunit. Treatment with LT-102 facilitated long-term potentiation in mouse hippocampal slices and reversed cognitive deficits in a phencyclidine-induced mouse model. Additionally, LT-102 treatment increased the protein level of brain-derived neurotrophic factor and the phosphorylation of GluA1 in primary neurons and hippocampal tissues.

CONCLUSION

We conclude that LT-102 ameliorates cognitive impairments in a phencyclidine-induced model of schizophrenia by enhancing synaptic function, which could make it a potential therapeutic candidate for CIAS.

Psychedelics for alzheimer's disease-related dementia: Unveiling therapeutic possibilities and pathways

Psychedelics have traditionally been used for spiritual and recreational purposes, but recent developments in psychotherapy have highlighted their potential as therapeutic agents. These compounds, which act as potent 5-hydroxytryptamine (5HT) agonists, have been recognized for their ability to enhance neural plasticity through the activation of the serotoninergic and glutamatergic systems. However, the implications of these findings for the treatment of neurodegenerative disorders, particularly dementia, have not been fully explored. In recent years, studies have revealed the modulatory and beneficial effects of psychedelics in the context of dementia, specifically Alzheimer's disease (AD)-related dementia, which lacks a definitive cure. Psychedelics such as N,N-dimethyltryptamine (DMT), lysergic acid diethylamide (LSD), and Psilocybin have shown potential in mitigating the effects of this debilitating disease. These compounds not only target neurotransmitter imbalances but also act at the molecular level to modulate signalling pathways in AD, including the brain-derived neurotrophic factor signalling pathway and the subsequent activation of mammalian target of rapamycin and other autophagy regulators. Therefore, the controlled and dose-dependent administration of psychedelics represents a novel therapeutic intervention worth exploring and considering for the development of drugs for the treatment of AD-related dementia. In this article, we critically examined the literature that sheds light on the therapeutic possibilities and pathways of psychedelics for AD-related dementia. While this emerging field of research holds great promise, further studies are necessary to elucidate the long-term safety, efficacy, and optimal treatment protocols. Ultimately, the integration of psychedelics into the current treatment paradigm may provide a transformative approach for addressing the unmet needs of individuals living with AD-related dementia and their caregivers.

Calcium-permeable AMPA and kainate receptors of GABAergic neurons

This Commentary presents a brief discussion of the action of glutamate calcium permeable receptors present with neurons on the release of the neurotransmitter gamma-aminobutyric acid (GABA). In particular, Glutamate sensitive Kainic Acid Receptors (KARs) and α-Amino-3-hydroxy-5-Methyl-4-isoxazole Propionic Acid Receptor (AMPARs) are Na+ channels that typically cause neuronal cells to depolarize and release GABA. Some of these receptors are also permeable to Ca2+ and are hence involved in the calcium-dependent release of GABA neurotransmitters. Calcium-permeable kainate and AMPA receptors (CP-KARs and CP-AMPARs) are predominantly located in GABAergic neurons in the mature brain and their primary role is to regulate GABA release. AMPARs which do not contain the GluA2 subunit are mainly localized in the postsynaptic membrane. CP-KAR receptors are located mainly in the presynapse. GABAergic neurons expressing CP-KARs and CP-AMPARs respond to excitation earlier and faster, suppressing hyperexcitation of other neurons by the advanced GABA release due to an early rapid [Ca2+]i increase. CP-AMPARs have demonstrated a more pronounced impact on plasticity compared to NMDARs because of their capacity to elevate intracellular Ca2+ levels independently of voltage. GABAergic neurons that express CP-AMPARs contribute to the disinhibition of glutamatergic neurons by suppressing GABAergic neurons that express CP-KARs. Hence, the presence of glutamate CP-KARs and CP-AMPARs is crucial in governing hyperexcitation and synaptic plasticity in GABAergic neurons.

Amnesia after Repeated Head Impact Is Caused by Impaired Synaptic Plasticity in the Memory Engram

Subconcussive head impacts are associated with the development of acute and chronic cognitive deficits. We recently reported that high-frequency head impact (HFHI) causes chronic cognitive deficits in mice through synaptic changes. To better understand the mechanisms underlying HFHI-induced memory decline, we used TRAP2/Ai32 transgenic mice to enable visualization and manipulation of memory engrams. We labeled the fear memory engram in male and female mice exposed to an aversive experience and subjected them to sham or HFHI. Upon subsequent exposure to natural memory recall cues, sham, but not HFHI, mice successfully retrieved fearful memories. In sham mice the hippocampal engram neurons exhibited synaptic plasticity, evident in amplified AMPA:NMDA ratio, enhanced AMPA-weighted tau, and increased dendritic spine volume compared with nonengram neurons. In contrast, although HFHI mice retained a comparable number of hippocampal engram neurons, these neurons did not undergo synaptic plasticity. This lack of plasticity coincided with impaired activation of the engram network, leading to retrograde amnesia in HFHI mice. We validated that the memory deficits induced by HFHI stem from synaptic plasticity impairments by artificially activating the engram using optogenetics and found that stimulated memory recall was identical in both sham and HFHI mice. Our work shows that chronic cognitive impairment after HFHI is a result of deficiencies in synaptic plasticity instead of a loss in neuronal infrastructure, and we can reinstate a forgotten memory in the amnestic brain by stimulating the memory engram. Targeting synaptic plasticity may have therapeutic potential for treating memory impairments caused by repeated head impacts.

Pattern sensitivity of ampakine-hypoxia interactions for evoking phrenic motor facilitation in anesthetized rat

Repeated hypoxic episodes can produce a sustained (>60 min) increase in neural drive to the diaphragm. The requirement of repeated hypoxic episodes (vs. a single episode) to produce phrenic motor facilitation (pMF) can be removed by allosteric modulation of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors using ampakines. We hypothesized that the ampakine-hypoxia interaction resulting in pMF requires that ampakine dosing precedes the onset of hypoxia. Phrenic nerve recordings were made from urethane-anesthetized, mechanically ventilated, and vagotomized adult male Sprague-Dawley rats during isocapnic conditions. Ampakine CX717 (15 mg/kg iv) was given immediately before (n = 8), during (n = 8), or immediately after (n = 8) a 5-min hypoxic episode (arterial oxygen partial pressure 40-45 mmHg). Ampakine before hypoxia (Aprior) resulted in a sustained increase in inspiratory phrenic burst amplitude (i.e., pMF) reaching +70 ± 21% above baseline (BL) after 60 min. This was considerably greater than corresponding values in the groups receiving ampakine during hypoxia (+28 ± 47% above BL, P = 0.005 vs. Aprior) or after hypoxia (+23 ± 40% above BL, P = 0.005 vs. Aprior). Phrenic inspiratory burst rate, heart rate, and systolic, diastolic, and mean arterial pressure (mmHg) were similar across the three treatment groups (all P > 0.3, treatment effect). We conclude that the presentation order of ampakine and hypoxia impacts the magnitude of pMF, with ampakine pretreatment evoking the strongest response. Ampakine pretreatment may have value in the context of hypoxia-based neurorehabilitation strategies.NEW & NOTEWORTHY Phrenic motor facilitation (pMF) is evoked after repeated episodes of brief hypoxia. pMF can also be induced when an allosteric modulator of AMPA receptors (ampakine) is intravenously delivered immediately before a single brief hypoxic episode. Here we show that ampakine delivery before hypoxia (vs. during or after hypoxia) evokes the largest pMF with minimal impact on arterial blood pressure and heart rate. Ampakine pretreatment may have value in the context of hypoxia-based neurorehabilitation strategies.

Synthesis of [11C]BIIB104, an α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic-Acid-Positive Allosteric Modulator, and Evaluation of the Bio-Distribution in Non-Human Primate Brains Using Positron Emission Tomography

The aim of this study was to measure the brain penetrance and kinetics of BIIB104, a first-in-class AMPA receptor potentiator developed for cognitive impairment associated with schizophrenia. It was recently halted in phase 2 clinical development, and there are a lack of tools to directly measure AMPA receptor engagement. To achieve this, the drug candidate was radiolabeled with carbon-11, and its brain penetrance and kinetics were measured in non-human primates via dynamic PET scans. Radiolabeling was achieved through a three-step nucleophilic [11C]cyanation reaction in one pot, resulting in the high radioactivity and radiochemical purity (>99%) of [11C]BIIB104. The study found that [11C]BIIB104 entered the non-human primate brains at 4-5% ID at peak, with a homogeneous distribution. However, a mild regional heterogeneity was observed in the thalamus. The lack of conclusive evidence for a change in regional values after BIIB104 dosing suggests that any specific binding component of BIIB104 is negligible compared to the free and non-specific components in the living brain. Overall, the study demonstrated high brain uptake with minor variability in [11C]BIIB104 distribution across various brain regions, its kinetics were consistent with those of passive diffusion, and the dominating components were the free concentration and non-specific binding. This information is valuable for understanding the potential effects and mechanisms of BIIB104 in the brain.

CRISPR-Cas9-generated PTCHD1 2489T>G stem cells recapitulate patient phenotype when undergoing neural induction

An estimated 3.5%-5.9% of the global population live with rare diseases, and approximately 80% of these diseases have a genetic cause. Rare genetic diseases are difficult to diagnose, with some affected individuals experiencing diagnostic delays of 5-30 years. Next-generation sequencing has improved clinical diagnostic rates to 33%-48%. In a majority of cases, novel variants potentially causing the disease are discovered. These variants require functional validation in specialist laboratories, resulting in a diagnostic delay. In the interim, the finding is classified as a genetic variant of uncertain significance (VUS) and the affected individual remains undiagnosed. A VUS (PTCHD1 c. 2489T>G) was identified in a child with autistic behavior, global developmental delay, and hypotonia. Loss of function mutations in PTCHD1 are associated with autism spectrum disorder and intellectual disability; however, the molecular function of PTCHD1 and its role in neurodevelopmental disease is unknown. Here, we apply CRISPR gene editing and induced pluripotent stem cell (iPSC) neural disease modeling to assess the variant. During differentiation from iPSCs to neural progenitors, we detect subtle but significant gene signatures in synaptic transmission and muscle contraction pathways. Our work supports the causal link between the genetic variant and the child's phenotype, providing evidence for the variant to be considered a pathogenic variant according to the American College of Medical Genetics and Genomics guidelines. In addition, our study provides molecular data on the role of PTCHD1 in the context of other neurodevelopmental disorders.

Phosphorylation of 4.1N by CaMKII Regulates the Trafficking of GluA1-containing AMPA Receptors During Long-term Potentiation in Acute Rat Hippocampal Brain Slices

OBJECTIVE

GluA1-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (AMPARs) inserted into postsynaptic membranes are key to the process of long-term potentiation (LTP). Some evidence has shown that 4.1N plays a critical role in the membrane trafficking of AMPARs. However, the underlying mechanism behind this is still unclear. We investigated the role of 4.1N-mediated membrane trafficking of AMPARs during theta-burst stimulation long-term potentiation (TBS-LTP), to illustrate the molecular mechanism behind LTP.

METHODS

LTP was induced by TBS in rat hippocampal CA1 neuron. Tat-GluA1 (MPR), which disrupts the association of 4.1N-GluA1, and autocamtide-2-inhibitory peptide, myristoylated (Myr-AIP), a CaMKII antagonist, were used to explore the role of 4.1N in the AMPARs trafficking during TBS-induced LTP. Immunoprecipitation (IP) and immunoblotting (IB)were used to detect protein expression, phosphorylation, and the interaction of p-CaMKII-4.1N-GluA1.

RESULTS

We found that Myr-AIP attenuated increases of p-CaMKII (T286), p-GluA1 (ser831), and 4.1N phosphorylation after TBS-LTP, and decreased the association of p-CaMKII-4.1N-GluA1, along with the expression of GluA1, at postsynaptic densities during TBS-LTP. We also designed interfering peptides to disrupt the interaction between 4.1N and GluA1, which showed that Tat-GluA1 (MPR) or Myr-AIP inhibited TBS-LTP and attenuated increases of GluA1 at postsynaptic sites, while Tat-GluA1 (MPR) or Myr-AIP had no effects on miniature excitatory postsynaptic currents (mEPSCs) in non-stimulated hippocampal CA1 neurons.

CONCLUSION

Active CaMKII enhanced the phosphorylation of 4.1N and facilitated the association of p-CaMKII with 4.1N-GluA1, which in turn resulted in GluA1 trafficking during TBS-LTP. The association of 4.1N-GluA1 is required for LTP, but not for basal synaptic transmission.

Proposed mechanisms of tau: relationships to traumatic brain injury, Alzheimer's disease, and epilepsy

Traumatic brain injury (TBI), Alzheimer's disease (AD), and epilepsy share proposed mechanisms of injury, including neuronal excitotoxicity, cascade signaling, and activation of protein biomarkers such as tau. Although tau is typically present intracellularly, in tauopathies, phosphorylated (p-) and hyper-phosphorylated (hp-) tau are released extracellularly, the latter leading to decreased neuronal stability and neurofibrillary tangles (NFTs). Tau cleavage at particular sites increases susceptibility to hyper-phosphorylation, NFT formation, and eventual cell death. The relationship between tau and inflammation, however, is unknown. In this review, we present evidence for an imbalanced endoplasmic reticulum (ER) stress response and inflammatory signaling pathways resulting in atypical p-tau, hp-tau and NFT formation. Further, we propose tau as a biomarker for neuronal injury severity in TBI, AD, and epilepsy. We present a hypothesis of tau phosphorylation as an initial acute neuroprotective response to seizures/TBI. However, if the underlying seizure pathology or TBI recurrence is not effectively treated, and the pathway becomes chronically activated, we propose a "tipping point" hypothesis that identifies a transition of tau phosphorylation from neuroprotective to injurious. We outline the role of amyloid beta (Aβ) as a "last ditch effort" to revert the cell to programmed death signaling, that, when fails, transitions the mechanism from injurious to neurodegenerative. Lastly, we discuss targets along these pathways for therapeutic intervention in AD, TBI, and epilepsy.

Pathophysiological Effects of Autoantibodies in Autoimmune Encephalitides

The heterogeneity of autoantibody targets in autoimmune encephalitides presents a challenge for understanding cellular and humoral pathophysiology, and the development of new treatment strategies. Thus, current treatment aims at autoantibody removal and immunosuppression, and is primarily based on data generated from other autoimmune neurological diseases and expert consensus. There are many subtypes of autoimmune encephalitides, which now entails both diseases with autoantibodies targeting extracellular antigens and classical paraneoplastic syndromes with autoantibodies targeting intracellular antigens. Here, we review the current knowledge of molecular and cellular effects of autoantibodies associated with autoimmune encephalitis, and evaluate the evidence behind the proposed pathophysiological mechanisms of autoantibodies in autoimmune encephalitis.

Evaluation of thiadiazine-based PET radioligands for imaging the AMPA receptor

As a subclass of ionotropic glutamate receptors (iGluRs), α-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid (AMPA) receptors have been implicated in various neurological disorders and neurodegenerative diseases. To further our understanding of AMPA receptor-related disorders in the central nervous system (CNS), it is important to be able to image and quantify AMPA receptors in vivo. In this study, we identified a novel F-containing AMPA positive allosteric modulator (PAM) 6 as a potential lead compound. Molecular docking studies and CNS PET multi-parameter optimization (MPO) analysis were used to predict the absorption, distribution, metabolism, and excretion (ADME) characteristics of 6 as a PET probe. The resulting PET probe, [18F]6 (codename [18F]AMPA-2109), was successfully radiolabeled and demonstrated excellent blood-brain barrier (BBB) permeability and high brain uptake in rodents and non-human primates. However, [18F]6 did not show substantial specific binding in the rodent or non-human primate brain. Further medicinal chemistry efforts are necessary to improve specific binding, and our work may serve as a starting point for the design of novel 18F-labeled AMPA receptor-targeted PET radioligands aimed for clinical translation.

Potential neuroprotective effect of nanomicellar curcumin on learning and memory functions following subacute exposure to bisphenol A in adult male rats

Bisphenol A (BPA) is an endocrine-disrupting chemical commonly utilized in the manufacture of plastics, which may cause damage to brain tissue. Curcumin is a phytochemical with protective effects against neurological and mental diseases. The purpose of this research was to evaluate whether nanomicellar curcumin (NmCur) might protect rats against BPA-induced learning and memory deficits. After determining the proper dose of BPA, the animals were randomly divided into 8 groups (8 rats in each group) receiving dextrose 5% (as vehicle of NmCur) (Dex), sesame oil (as vehicle of BPA) (Sea), Sea plus Dex, NmCur (50 mg/kg), BPA (50 mg/kg), and 50 mg/kg BPA plus 10, 25, and 50 mg/kg NmCur groups, respectively. Behavioral tests performed using passive avoidance training (PAT), open-field (OF), and Morris water maze (MWM) tests. The expression of oxidative stress markers, proinflammatory cytokines, oxidative stress-scavenging enzymes, glutamate receptors, and MAPK and memory-related proteins was measured in rat hippocampus and cortical tissues. BPA up-regulated ROS, MDA, TNF-α, IL-6, IL-1β, SOD, GST, p-P38, and p-JNK levels; however, it down-regulated GSH, GPx, GR, CAT, p-AKT, p-ERK1/2, p-NR1, p-NR2A, p-NR2B, p-GluA1, p-CREB, and BDNF levels. BPA decreased step-through latency (STL) and peripheral and total, but not central, locomotor activity. It increased the time to find the hidden platform, the mean of escape latency time, and the traveled distance in the target quadrant, but decreased the time spent in the target quadrant. The combination of BPA (50 mg/kg) and NmCur (25 and 50 mg/kg) reversed all of BPA's adverse effects. Therefore, NmCur exhibited neuroprotective effects against subacute BPA-caused learning and memory impairment.

Neuroplasticity of the extended amygdala in opioid withdrawal and prolonged opioid abstinence

Opioid use disorder is characterized by excessive use of opioids, inability to control its use, a withdrawal syndrome upon discontinuation of opioids, and long-term likelihood of relapse. The behavioral stages of opioid addiction correspond with affective experiences that characterize the opponent process view of motivation. In this framework, active involvement is accompanied by positive affective experiences which gives rise to "reward craving," whereas the opponent process, abstinence, is associated with the negative affective experiences that produce "relief craving." Relief craving develops along with a hypersensitization to the negatively reinforcing aspects of withdrawal during abstinence from opioids. These negative affective experiences are hypothesized to stem from neuroadaptations to a network of affective processing called the "extended amygdala." This negative valence network includes the three core structures of the central nucleus of the amygdala (CeA), the bed nucleus of the stria terminalis (BNST), and the nucleus accumbens shell (NAc shell), in addition to major inputs from the basolateral amygdala (BLA). To better understand the major components of this system, we have reviewed their functions, inputs and outputs, along with the associated neural plasticity in animal models of opioid withdrawal. These models demonstrate the somatic, motivational, affective, and learning related models of opioid withdrawal and abstinence. Neuroadaptations in these stress and motivational systems are accompanied by negative affective and aversive experiences that commonly give rise to relapse. CeA neuroplasticity accounts for many of the aversive and fear-related effects of opioid withdrawal via glutamatergic plasticity and changes to corticotrophin-releasing factor (CRF)-containing neurons. Neuroadaptations in BNST pre-and post-synaptic GABA-containing neurons, as well as their noradrenergic modulation, may be responsible for a variety of aversive affective experiences and maladaptive behaviors. Opioid withdrawal yields a hypodopaminergic and amotivational state and results in neuroadaptive increases in excitability of the NAc shell, both of which are associated with increased vulnerability to relapse. Finally, BLA transmission to hippocampal and cortical regions impacts the perception of conditioned aversive effects of opioid withdrawal by higher executive systems. The prevention or reversal of these varied neuroadaptations in the extended amygdala during opioid withdrawal could lead to promising new interventions for this life-threatening condition.

A human in vitro neuronal model for studying homeostatic plasticity at the network level

Mechanisms that underlie homeostatic plasticity have been extensively investigated at single-cell levels in animal models, but are less well understood at the network level. Here, we used microelectrode arrays to characterize neuronal networks following induction of homeostatic plasticity in human induced pluripotent stem cell (hiPSC)-derived glutamatergic neurons co-cultured with rat astrocytes. Chronic suppression of neuronal activity through tetrodotoxin (TTX) elicited a time-dependent network re-arrangement. Increased expression of AMPA receptors and the elongation of axon initial segments were associated with increased network excitability following TTX treatment. Transcriptomic profiling of TTX-treated neurons revealed up-regulated genes related to extracellular matrix organization, while down-regulated genes related to cell communication; also astrocytic gene expression was found altered. Overall, our study shows that hiPSC-derived neuronal networks provide a reliable in vitro platform to measure and characterize homeostatic plasticity at network and single-cell levels; this platform can be extended to investigate altered homeostatic plasticity in brain disorders.

Glutamate Receptor Dysregulation and Platelet Glutamate Dynamics in Alzheimer's and Parkinson's Diseases: Insights into Current Medications

Two of the most prevalent neurodegenerative disorders (NDDs), Alzheimer's disease (AD) and Parkinson's disease (PD), present significant challenges to healthcare systems worldwide. While the etiologies of AD and PD differ, both diseases share commonalities in synaptic dysfunction, thereby focusing attention on the role of neurotransmitters. The possible functions that platelets may play in neurodegenerative illnesses including PD and AD are becoming more acknowledged. In AD, platelets have been investigated for their ability to generate amyloid-ß (Aß) peptides, contributing to the formation of neurotoxic plaques. Moreover, platelets are considered biomarkers for early AD diagnosis. In PD, platelets have been studied for their involvement in oxidative stress and mitochondrial dysfunction, which are key factors in the disease's pathogenesis. Emerging research shows that platelets, which release glutamate upon activation, also play a role in these disorders. Decreased glutamate uptake in platelets has been observed in Alzheimer's and Parkinson's patients, pointing to a systemic dysfunction in glutamate handling. This paper aims to elucidate the critical role that glutamate receptors play in the pathophysiology of both AD and PD. Utilizing data from clinical trials, animal models, and cellular studies, we reviewed how glutamate receptors dysfunction contributes to neurodegenerative (ND) processes such as excitotoxicity, synaptic loss, and cognitive impairment. The paper also reviews all current medications including glutamate receptor antagonists for AD and PD, highlighting their mode of action and limitations. A deeper understanding of glutamate receptor involvement including its systemic regulation by platelets could open new avenues for more effective treatments, potentially slowing disease progression and improving patient outcomes.

Uncovering the Significance of STEP61 in Alzheimer's Disease: Structure, Substrates, and Interactome

STEP (STriatal-Enriched Protein Tyrosine Phosphatase) is a brain-specific phosphatase that plays an important role in controlling signaling molecules involved in neuronal activity and synaptic development. The striatum is the main location of the STEP enzyme. An imbalance in STEP61 activity is a risk factor for Alzheimer's disease (AD). It can contribute to the development of numerous neuropsychiatric diseases, including Parkinson's disease (PD), schizophrenia, fragile X syndrome (FXS), Huntington's disease (HD), alcoholism, cerebral ischemia, and stress-related diseases. The molecular structure, chemistry, and molecular mechanisms associated with STEP61's two major substrates, Alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPAr) and N-methyl-D-aspartate receptors (NMDARs), are crucial in understanding the relationship between STEP61 and associated illnesses. STEP's interactions with its substrate proteins can alter the pathways of long-term potentiation and long-term depression. Therefore, understanding the role of STEP61 in neurological illnesses, particularly Alzheimer's disease-associated dementia, can provide valuable insights for possible therapeutic interventions. This review provides valuable insights into the molecular structure, chemistry, and molecular mechanisms associated with STEP61. This brain-specific phosphatase controls signaling molecules involved in neuronal activity and synaptic development. This review can aid researchers in gaining deep insights into the complex functions of STEP61.

The Effects of Ninjinyoeito on Impaired Spatial Memory and Prefrontal Cortical Synaptic Plasticity through α-Amino-3-hydroxy-5-4-isoxazole Propionic Acid Receptor Subunit in a Rat Model with Cerebral Ischemia and β-Amyloid Injection

Ninjinyoeito (NYT), a traditional Japanese medicine, is effective for improving physical strength and treating fatigue and anorexia. Recently, a clinical report revealed that NYT ameliorates cognitive dysfunction in Alzheimer's disease (AD) patients, although the mechanisms remain unclear. AD is a neurodegenerative disorder accompanied by a progressive deficit in memory. Current therapeutic agents are largely ineffective in treating cognitive dysfunction in AD patients. In this study, we investigated the effects of NYT on spatial memory impairment in a rat model of dementia. Rats were prepared with transient cerebral ischemia and intraventricular injection of β-amyloid1-42 for 7 days (CI + Aβ). NYT was orally administered for 7 days after cerebral ischemia. We evaluated spatial memory using the Morris water maze and investigated the expression of α-amino-3-hydroxy-5-4-isoxazole propionic acid receptor subunits, the phosphorylation level of glutamate receptor A (GluA)1 at serine sites S831 and S845, and the Ca2+/calmodulin-dependent protein kinase II (CaMKII) in the hippocampus and prefrontal cortex of CI + Aβ rats. In the CI + Aβ rats, NYT treatment shortened the extended time to reach the platform. However, NYT did not restore the decrease in the hippocampal GluA1, GluA2, or CaMKII expression but increased prefrontal cortical phosphorylation levels of S845-GluA1 and CaMKII. Therefore, NYT may alleviate spatial memory impairment by promoting glutamatergic transmission involved in the phosphorylation of S845-GluA1 and CaMKII in the prefrontal cortex of CI + Aβ rats. Our results suggest that NYT is a valuable treatment for AD patients.

Electrophysiological Assessment of Newly Synthesized 2,3-Benzodiazepine Derivatives for Inhibiting the AMPA Receptor Channel

Three major subtypes of ionotropic receptors regulate glutamatergic synaptic transmission, one of which is α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors (AMPARs). They are tetrameric, cation-permeable ionotropic glutamate receptors found across the brain. Abnormalities in AMPA receptor trafficking and synaptic assembly are linked to cognitive decline and neurological diseases such as Alzheimer's, Parkinson's, and Huntington's. The present study will investigate the effects of four novel 2,3-benzodiazepine derivatives on AMPA receptor subunits by comparing their effects on synaptic responses, desensitization, and deactivation rate in human embryonic kidney cells (HEK293T) recombinant AMPAR subunits using whole-cell patch-clamp electrophysiology. All four 2,3-BDZ compounds showed inhibitory activity against all the homomeric and heteromeric subunits tested. While the desensitization and deactivation rates in 2,3-BDZ-1 and 2,3-BDZ-2 decreased and increased, respectively, in the other two compounds (i.e., 2,3-BDZ-3 and 2,3-BDZ-4), there was no change in the desensitization or deactivation rates. These results contribute to a better understanding of AMPARs by identifying potential 2,3-BDZ drugs that demonstrate inhibitory effects on the AMPAR subunits.

Bio-enhanced fraction from Clitoria ternatea root extract ameliorates cognitive functions and in vivo hippocampal neuroplasticity in chronic cerebral hypoperfusion rat model

Research employing a bio-enhanced fraction of Clitoria ternatea (CT) to treat cognitive decline in the animal model has not yet been found. This study aimed to determine the neuroprotective effect of CT root bioactive fraction (CTRF) in chronic cerebral hypoperfusion (CCH) rat model. CTRF and its major compound, clitorienolactones A (CLA), were obtained using column chromatography. A validated HPLC-UV method was employed for the standardization of CTRF. CCH rats were given orally either vehicle or fraction (10, 20 and 40 mg/kg). Behavioural and hippocampal neuroplasticity studies were conducted following 4 weeks post-surgery. The brain hippocampus was extracted for proteins and neurotransmitters analyses. HPLC analysis showed that CTRF contained 25% (w/w) of CLA. All tested doses of CTRF and CLA (10 mg/kg) significantly restored cognitive deficits and reversed the inhibition of neuroplasticity by CCH. However, only CTRF (40 mg/kg) and CLA (10 mg/kg) significantly reversed the elevation of amyloid-beta plaque. Subsequently, treatment with CTRF (40 mg/kg) and CLA (10 mg/kg) alleviated the downregulation of molecular synaptic signalling proteins levels caused by CCH. The neurotransmitters level was restored following treatment of CTRF and CLA. Our finding suggested that CTRF improves memory and neuroplasticity in CCH rats which was mainly contributed by CLA.

Interventional Mental Health: A Transdisciplinary Approach to Novel Psychiatric Care Delivery

Mental health disorders are among the most common health conditions in the United States. Traditional clinical treatments rely on psychiatric counseling and, in many cases, prescription medications. We propose an innovative model, Interventional Mental Health, which employs a combination of modalities through a multifaceted approach to treat conditions that have exhibited limited responsiveness to traditional methods and individuals afflicted with multiple comorbidities simultaneously. We hypothesize that creating a unique treatment algorithm combining current therapeutic modalities such as Stellate Ganglion Blocks (SGB), Transcranial Magnetic Stimulation (TMS) therapy, and ketamine therapy, within a consolidated timeframe, will yield synergistic outcomes among patients presenting with comorbid post-traumatic stress disorder (PTSD), depression, and/or anxiety.

Pathophysiology of Cerebellar Degeneration in Mitochondrial Disorders: Insights from the Harlequin Mouse

By means of a proteomic approach, we assessed the pathways involved in cerebellar neurodegeneration in a mouse model (Harlequin, Hq) of mitochondrial disorder. A differential proteomic profile study (iTRAQ) was performed in cerebellum homogenates of male Hq and wild-type (WT) mice 8 weeks after the onset of clear symptoms of ataxia in the Hq mice (aged 5.2 ± 0.2 and 5.3 ± 0.1 months for WT and Hq, respectively), followed by a biochemical validation of the most relevant changes. Additional groups of 2-, 3- and 6-month-old WT and Hq mice were analyzed to assess the disease progression on the proteins altered in the proteomic study. The proteomic analysis showed that beyond the expected deregulation of oxidative phosphorylation, the cerebellum of Hq mice showed a marked astroglial activation together with alterations in Ca²⁺ homeostasis and neurotransmission, with an up- and downregulation of GABAergic and glutamatergic neurotransmission, respectively, and the downregulation of cerebellar "long-term depression", a synaptic plasticity phenomenon that is a major player in the error-driven learning that occurs in the cerebellar cortex. Our study provides novel insights into the mechanisms associated with cerebellar degeneration in the Hq mouse model, including a complex deregulation of neuroinflammation, oxidative phosphorylation and glutamate, GABA and amino acids' metabolism.

Mechanisms of mGluR-dependent plasticity in hippocampal area CA2

Pyramidal cells in hippocampal area CA2 have synaptic properties that are distinct from the other CA subregions. Notably, this includes a lack of typical long-term potentiation of stratum radiatum synapses. CA2 neurons express high levels of several known and potential regulators of metabotropic glutamate receptor (mGluR)-dependent signaling including Striatal-Enriched Tyrosine Phosphatase (STEP) and several Regulator of G-protein Signaling (RGS) proteins, yet the functions of these proteins in regulating mGluR-dependent synaptic plasticity in CA2 are completely unknown. Thus, the aim of this study was to examine mGluR-dependent synaptic depression and to determine whether STEP and the RGS proteins RGS4 and RGS14 are involved. Using whole cell voltage-clamp recordings from mouse pyramidal cells, we found that mGluR agonist-induced long-term depression (mGluR-LTD) is more pronounced in CA2 compared with that observed in CA1. This mGluR-LTD in CA2 was found to be protein synthesis and STEP dependent, suggesting that CA2 mGluR-LTD shares mechanistic processes with those seen in CA1, but in addition, RGS14, but not RGS4, was essential for mGluR-LTD in CA2. In addition, we found that exogenous application of STEP could rescue mGluR-LTD in RGS14 KO slices. Supporting a role for CA2 synaptic plasticity in social cognition, we found that RGS14 KO mice had impaired social recognition memory as assessed in a social discrimination task. These results highlight possible roles for mGluRs, RGS14, and STEP in CA2-dependent behaviors, perhaps by biasing the dominant form of synaptic plasticity away from LTP and toward LTD in CA2.

The effect of Lavandula Coronopifolia essential oil on the biophysical properties of desensitization and deactivation gating currents in ionotropic receptors

The rising incidence of cancer and the lack of effective therapeutic interventions for many neurological illnesses like Alzheimer's and epilepsy has prompted us to investigate the composition and effects of the Lavandula coronopifolia oil from Palestine on cancer cells and AMPA receptor subunits in the brain due to the vast range of beneficial properties of Lavandula coronopifolia essential oil (EO). GC/MS was used to analyze L. coronopifolia's EO chemistry. EO's cytotoxicity and biophysical effects on AMPA receptors were investigated using MTS and electrophysiological techniques. The GC-MS results revealed that L. coronopifolia EO has a high content of eucalyptol (77.23%), β-pinene (6.93%), and α-pinene (4.95%). The EO showed more significant antiproliferative selectivity activities against HepG2 cancer cell lines than HEK293T cell lines with IC₅₀ values of 58.51 and 133.22 µg/mL, respectively. The EO of L. coronopifolia affected AMPA receptor kinetics (desensitization and deactivation) and preferred homomeric GluA1 and heteromeric GluA1/A2 receptors. These findings indicate the potential therapeutic use of L. coronopifolia EO in the selective treatment of HepG2 cancer cell lines and neurodegenerative diseases.

Calcium Homeostasis, Transporters, and Blockers in Health and Diseases of the Cardiovascular System

Calcium is a highly positively charged ionic species. It regulates all cell types' functions and is an important second messenger that controls and triggers several mechanisms, including membrane stabilization, permeability, contraction, secretion, mitosis, intercellular communications, and in the activation of kinases and gene expression. Therefore, controlling calcium transport and its intracellular homeostasis in physiology leads to the healthy functioning of the biological system. However, abnormal extracellular and intracellular calcium homeostasis leads to cardiovascular, skeletal, immune, secretory diseases, and cancer. Therefore, the pharmacological control of calcium influx directly via calcium channels and exchangers and its outflow via calcium pumps and uptake by the ER/SR are crucial in treating calcium transport remodeling in pathology. Here, we mainly focused on selective calcium transporters and blockers in the cardiovascular system.

Synaptic logistics: Competing over shared resources

High turnover rates of synaptic proteins imply that synapses constantly need to replace their constituent building blocks. This requires sophisticated supply chains and potentially exposes synapses to shortages as they compete for limited resources. Interestingly, competition in neurons has been observed at different scales. Whether it is competition of receptors for binding sites inside a single synapse or synapses fighting for resources to grow. Here we review the implications of such competition for synaptic function and plasticity. We identify multiple mechanisms that synapses use to safeguard themselves against supply shortages and identify a fundamental neurologistic trade-off governing the sizes of reserve pools of essential synaptic building blocks.

Mathematical Model of Synaptic Long-Term Potentiation as a Bistability in a Chain of Biochemical Reactions with a Positive Feedback

Nitric oxide (NO) is involved in synaptic long-term potentiation (LTP) by multiple signaling pathways. Here, we show that LTP of synaptic transmission can be explained as a feature of signal transduction-bistable behavior in a chain of biochemical reactions with positive feedback, formed by diffusion of NO to the presynaptic site and facilitating the release of glutamate (Glu). The dynamics of Glu, calcium (Ca²⁺) and NO is described by a system of nonlinear reaction-diffusion equations with modified Michaelis-Menten (MM) kinetics. Numerical investigation reveals that the chain of biochemical reactions analyzed can exhibit a bistable behavior under physiological conditions when production of Glu is described by MM kinetics and decay of NO is modeled by means of two enzymatic pathways with different kinetic properties. Our finding extends understanding of the role of NO in LTP: a short high-intensity stimulus is "memorized" as a long-lasting elevation of NO concentration. The conclusions obtained by analysis of the chain of biochemical reactions describing LTP can be generalized to other chains of interactions or for creating the logical elements for biological computers.

Exposure to Tetrabutylammonium Bromide Impairs Cranial Neural Crest Specification, Neurogenic Program, and Brain Morphogenesis

Tetrabutylammonium bromide (TBAB) is a widely used industrial reagent and is commonly found in our aquatic ecosystem as an industrial byproduct. In humans, the ingestion of TBAB causes severe neurological impairments and disorders such as vertigo, hallucinations, and delirium. Yet, the extent of environmental risk and TBAB toxicity to human health is poorly understood. In this study, we aim to determine the developmental toxicity of TBAB using zebrafish embryos as a model and provide novel insights into the mechanism of action of such chemicals on neurodevelopment and the overall embryonic program. Our results show that exposure to TBAB results in impaired development of the brain, inner ear, and pharyngeal skeletal elements in the zebrafish embryo. TBAB treatment resulted in aberrations in the specification of the neural crest precursors, hindbrain segmentation, and otic neurogenesis. TBAB treatment also induced a surge in apoptosis in the head, tail, and trunk regions of the developing embryo. Long-term TBAB exposure resulted in cardiac edema and craniofacial defects. Further, in silico molecular docking analysis indicated that TBAB binds to AMPA receptors and modulates neural developmental genes such as olfactomedin and acetylcholinesterase in the embryonic brain. To summarize, our study highlights the novel effects of TBAB on embryonic brain formation and segmentation, ear morphogenesis, and craniofacial skeletal development.

Peptide-PAINT Using a Transfected-Docker Enables Live- and Fixed-Cell Super-Resolution Imaging

Point accumulation for imaging in nanoscale topography (PAINT) is a single-molecule technique for super-resolution microscopy, which uses exchangeable single stranded DNA oligos or peptide-pairs to create blinking phenomenon and achieves ≈5-25 nanometer resolution. Here, it is shown that by transfecting the protein-of-interest with a docker-coil, rather than by adding the docker externally-as is the norm when using DNA tethers or antibodies as dockers-similar localization can be achieved, ≈10 nm. However, using a transfected docker has several experimental advances and simplifications. Most importantly, it allows Peptide-PAINT to be applied to transfected live cells for imaging surface proteins in mammalian cells and neurons under physiological conditions. The enhanced resolution of Peptide-PAINT is also shown for organelles in fixed cells to unravel structural details including ≈40-nm and ≈60-nm axial repeats in vimentin filaments in the cytoplasm, and fiber shapes of sub-100-nm histone-rich regions in the nucleus.

Dysregulation of AMPA Receptor Trafficking and Intracellular Vesicular Sorting in the Prefrontal Cortex of Dopamine Transporter Knock-Out Rats

Dopamine (DA) and glutamate interact, influencing neural excitability and promoting synaptic plasticity. However, little is known regarding the molecular mechanisms underlying this crosstalk. Since perturbation of DA-AMPA receptor interaction might sustain pathological conditions, the major aim of our work was to evaluate the effect of the hyperactive DA system on the AMPA subunit composition, trafficking, and membrane localization in the prefrontal cortex (PFC). Taking advantage of dopamine transporter knock-out (DAT−/−) rats, we found that DA overactivity reduced the translation of cortical AMPA receptors and their localization at both synaptic and extra-synaptic sites through, at least in part, altered intracellular vesicular sorting. Moreover, the reduced expression of AMPA receptor-specific anchoring proteins and structural markers, such as Neuroligin-1 and nCadherin, likely indicate a pattern of synaptic instability. Overall, these data reveal that a condition of hyperdopaminergia markedly alters the homeostatic plasticity of AMPA receptors, suggesting a general destabilization and depotentiation of the AMPA-mediated glutamatergic neurotransmission in the PFC. This effect might be functionally relevant for disorders characterized by elevated dopaminergic activity.

Muscarinic acetylcholine receptor-dependent and NMDA receptor-dependent LTP and LTD share the common AMPAR trafficking pathway

The forebrain cholinergic system promotes higher brain function in part by signaling through the M₁ muscarinic acetylcholine receptor (mAChR). Long-term potentiation (LTP) and long-term depression (LTD) of excitatory synaptic transmission in the hippocampus are also induced by mAChR. An AMPA receptor (AMPAR) trafficking model for hippocampal neurons has been proposed to simulate N-methyl-D-aspartate receptor (NMDAR)-dependent synaptic plasticity in the early phase. In this study, we demonstrated the validity of the hypothesis that the mAChR-dependent LTP/LTD shares a common AMPAR trafficking pathway associated with NMDAR-dependent LTP/LTD. However, unlike NMDAR, Ca²⁺ influx into the spine cytosol occurs owing to the Ca²⁺ stored inside the ER and is induced via the activation of inositol 1,4,5-trisphosphate (IP3) receptors during M1 mAChR activation. Moreover, the AMPAR trafficking model implies that alterations in LTP and LTD observed in Alzheimer's disease could be attributed to age-dependent reductions in AMPAR expression levels.

Synaptic Plasticity Abnormalities in Fetal Alcohol Spectrum Disorders

The brain's ability to strengthen or weaken synaptic connections is often termed synaptic plasticity. It has been shown to function in brain remodeling following different types of brain damage (e.g., drugs of abuse, alcohol use disorders, neurodegenerative diseases, and inflammatory conditions). Although synaptic plasticity mechanisms have been extensively studied, how neural plasticity can influence neurobehavioral abnormalities in alcohol use disorders (AUDs) is far from being completely understood. Alcohol use during pregnancy and its harmful effects on the developing offspring are major public health, social, and economic challenges. The significant attribute of prenatal alcohol exposure on offspring is damage to the central nervous system (CNS), causing a range of synaptic structural, functional, and behavioral impairments, collectively called fetal alcohol spectrum disorder (FASD). Although the synaptic mechanisms in FASD are limited, emerging evidence suggests that FASD pathogenesis involves altering a set of molecules involved in neurotransmission, myelination, and neuroinflammation. These studies identify several immediate and long-lasting changes using many molecular approaches that are essential for synaptic plasticity and cognitive function. Therefore, they can offer potential synaptic targets for the many neurobehavioral abnormalities observed in FASD. In this review, we discuss the substantial research progress in different aspects of synaptic and molecular changes that can shed light on the mechanism of synaptic dysfunction in FASD. Increasing our understanding of the synaptic changes in FASD will significantly advance our knowledge and could provide a basis for finding novel therapeutic targets and innovative treatment strategies.

Synapse Dysfunctions in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic neuroinflammatory disease of the central nervous system (CNS) affecting nearly three million humans worldwide. In MS, cells of an auto-reactive immune system invade the brain and cause neuroinflammation. Neuroinflammation triggers a complex, multi-faceted harmful process not only in the white matter but also in the grey matter of the brain. In the grey matter, neuroinflammation causes synapse dysfunctions. Synapse dysfunctions in MS occur early and independent from white matter demyelination and are likely correlates of cognitive and mental symptoms in MS. Disturbed synapse/glia interactions and elevated neuroinflammatory signals play a central role. Glutamatergic excitotoxic synapse damage emerges as a major mechanism. We review synapse/glia communication under normal conditions and summarize how this communication becomes malfunctional during neuroinflammation in MS. We discuss mechanisms of how disturbed glia/synapse communication can lead to synapse dysfunctions, signaling dysbalance, and neurodegeneration in MS.

Anti-AMPA Receptor Autoantibodies Reduce Excitatory Currents in Rat Hippocampal Neurons

The GluR3 subunit of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) has been identified as a target for autoantibodies (Aabs) in autoimmune encephalopathy and other diseases. Recent studies have proposed mechanisms by which these Aabs act, but their exact role in neuronal excitability is yet to be established. Patient Aabs have been shown to bind to specific regions within the GluR3 subunit. GLUR3B peptides were designed based on described (ELISA) immunogenic epitopes for Aabs and an immunisation strategy was used to generate novel anti-AMPAR Aabs. Target-specific binding and specificity of affinity-purified anti-AMPAR Aabs was confirmed using enzyme-linked immunosorbent assay, immunocytochemistry and Western blot. Functional anti-AMPAR Aab effects were determined on excitatory postsynaptic currents (EPSCs) from primary hippocampal neurons using whole-cell patch-clamp electrophysiology. Acute (10 or 30 min) or longer-term (24 h) application of anti-AMPAR Aabs caused a significant reduction in the mean frequency of spontaneous and miniature EPSCs in hippocampal neurons. Our data demonstrate that anti-AMPAR Aabs targeting peptides linked to auto-immune diseases mediate inhibitory effects on neuronal excitability at the synaptic level, such effects may lead to disruption of the excitatory/inhibitory balance at a network level.

Accumulation of pTau231 at the Postsynaptic Density in Early Alzheimer's Disease

BACKGROUND

Phosphorylated cytoplasmic tau inclusions correlate with and precede cognitive deficits in Alzheimer's disease (AD). However, pathological tau accumulation and relationships to synaptic changes remain unclear.

OBJECTIVE

To address this, we examined postmortem brain from 50 individuals with the full spectrum of AD (clinically and neuropathologically). Total tau, pTau231, and AMPA GluR1 were compared across two brain regions (entorhinal and middle frontal cortices), as well as clinically stratified groups (control, amnestic mild cognitive impairment, AD dementia), NIA-AA Alzheimer's Disease Neuropathologic Change designations (Not, Low, Intermediate, High), and Braak tangle stages (1-6). Significant co-existing pathology was excluded to isolate changes attributed to pathologic AD.

METHODS

Synaptosomal fractionation and staining were performed to measure changes in total Tau, pTau231, and AMPA GluR1. Total Tau and pTau231 were quantified in synaptosomal fractions using Quanterix Simoa HD-X.

RESULTS

Increasing pTau231 in frontal postsynaptic fractions correlated positively with increasing clinical and neuropathological AD severity. Frontal cortex is representative of early AD, as it does not become involved by tau tangles until late in AD. Entorhinal total tau was significantly higher in the amnestic mild cognitive impairment group when compared to AD, but only after accounting for AD associated synaptic changes. Alterations in AMPA GluR1 observed in the entorhinal cortex, but not middle frontal cortex, suggest that pTau231 mislocalization and aggregation in postsynaptic structures may impair glutamatergic signaling by promoting AMPA receptor dephosphorylation and internalization.

CONCLUSION

Results highlight the potential effectiveness of early pharmacological interventions targeting pTau231 accumulation at the postsynaptic density.

Electrophysiology of Dendritic Spines: Information Processing, Dynamic Compartmentalization, and Synaptic Plasticity

For many years, synaptic transmission was considered as information transfer between presynaptic neuron and postsynaptic cell. At the synaptic level, it was thought that dendritic arbors were only receiving and integrating all information flow sent along to the soma, while axons were primarily responsible for point-to-point information transfer. However, it is important to highlight that dendritic spines play a crucial role as postsynaptic components in central nervous system (CNS) synapses, not only integrating and filtering signals to the soma but also facilitating diverse connections with axons from many different sources. The majority of excitatory connections from presynaptic axonal terminals occurs on postsynaptic spines, although a subset of GABAergic synapses also targets spine heads. Several studies have shown the vast heterogeneous morphological, biochemical, and functional features of dendritic spines related to synaptic processing. In this chapter (adding to the relevant data on the biophysics of spines described in Chap. 1 of this book), we address the up-to-date functional dendritic characteristics assessed through electrophysiological approaches, including backpropagating action potentials (bAPs) and synaptic potentials mediated in dendritic and spine compartmentalization, as well as describing the temporal and spatial dynamics of glutamate receptors in the spines related to synaptic plasticity.

Lipid Raft Facilitated Receptor Organization and Signaling: A Functional Rheostat in Embryonic Development, Stem Cell Biology and Cancer

Molecular views of plasma membrane organization and dynamics are gradually changing over the past fifty years. Dynamics of plasma membrane instigate several signaling nexuses in eukaryotic cells. The striking feature of plasma membrane dynamics is that, it is internally transfigured into various subdomains of clustered macromolecules. Lipid rafts are nanoscale subdomains, enriched with cholesterol and sphingolipids, reside as floating entity mostly on the exoplasmic leaflet of the lipid bilayer. In terms of functionality, lipid rafts are unique among other membrane subdomains. Herein, advances on the roles of lipid rafts in cellular physiology and homeostasis are discussed, precisely, on how rafts dynamically harbor signaling proteins, including GPCRs, catalytic receptors, and ionotropic receptors within it and orchestrate multiple signaling pathways. In the developmental proceedings signaling are designed for patterning of overall organism and they differ from the somatic cell physiology and signaling of fully developed organisms. Some of the developmental signals are characteristic in maintenance of stemness and activated during several types of tumor development and cancer progression. The harmony between extracellular signaling and lineage specific transcriptional programs are extremely important for embryonic development. The roles of plasma membrane lipid rafts mediated signaling in lineage specificity, early embryonic development, stem cell maintenance are emerging. In view of this, we have highlighted and analyzed the roles of lipid rafts in receptor organization, cell signaling, and gene expression during embryonic development; from pre-implantation through the post-implantation phase, in stem cell and cancer biology.

Neuropharmacology of Alcohol Addiction with Special Emphasis on Proteomic Approaches for Identification of Novel Therapeutic Targets

Alcohol is a generic pharmacological agent with only a few recognized primary targets. Nmethyl- D-aspartate, gamma-aminobutyric acid, glycine, 5-hydroxytryptamine 3 (serotonin), nicotinic acetylcholine receptors, and L-type Ca2+ channels and G-protein-activated inwardly rectifying K channels are all involved. Following the first hit of alcohol on specific brain targets, the second wave of indirect effects on various neurotransmitter/neuropeptide systems begins, leading to the typical acute behavioral effects of alcohol, which range from disinhibition to sedation and even hypnosis as alcohol concentrations rise. Recent research has revealed that gene regulation is significantly more complex than previously thought and does not fully explain changes in protein levels. As a result, studying the proteome directly, which differs from the genome/transcriptome in terms of complexity and dynamicity, has provided unique insights into extraordinary advances in proteomic techniques that have changed the way we can analyze the composition, regulation, and function of protein complexes and pathways underlying altered neurobiological conditions. Neuroproteomics has the potential to revolutionize alcohol research by allowing researchers to gain a better knowledge of how alcohol impacts protein structure, function, connections, and networks on a global scale. The amount of information collected from these breakthroughs can aid in identifying valuable biomarkers for early detection and improved prognosis of an alcohol use disorder and future pharmaceutical targets for the treatment of alcoholism.

Synaptic plasticity and mental health: methods, challenges and opportunities

Activity-dependent synaptic plasticity is a ubiquitous property of the nervous system that allows neurons to communicate and change their connections as a function of past experiences. Through reweighting of synaptic strengths, the nervous system can remodel itself, giving rise to durable memories that create the biological basis for mental function. In healthy individuals, synaptic plasticity undergoes characteristic developmental and aging trajectories. Dysfunctional plasticity, in turn, underlies a wide spectrum of neuropsychiatric disorders including depression, schizophrenia, addiction, and posttraumatic stress disorder. From a mechanistic standpoint, synaptic plasticity spans the gamut of spatial and temporal scales, from microseconds to the lifespan, from microns to the entire nervous system. With the numbers and strengths of synapses changing on such wide scales, there is an important need to develop measurement techniques with complimentary sensitivities and a growing number of approaches are now being harnessed for this purpose. Through hemodynamic measures, structural and tracer imaging, and noninvasive neuromodulation, it is possible to image structural and functional changes that underlie synaptic plasticity and associated behavioral learning. Here we review the mechanisms of neural plasticity and the historical and future trends in techniques that allow imaging of synaptic changes that accompany psychiatric disorders, highlighting emerging therapeutics and the challenges and opportunities accompanying this burgeoning area of study.

Pleiotropic Ankyrins: Scaffolds for Ion Channels and Transporters

The ankyrin proteins (Ankyrin-R, Ankyrin-B, and Ankyrin-G) are a family of scaffolding, or membrane adaptor proteins necessary for the regulation and targeting of several types of ion channels and membrane transporters throughout the body. These include voltage-gated sodium, potassium, and calcium channels in the nervous system, heart, lungs, and muscle. At these sites, ankyrins recruit ion channels, and other membrane proteins, to specific subcellular domains, which are then stabilized through ankyrin's interaction with the submembranous spectrin-based cytoskeleton. Several recent studies have expanded our understanding of both ankyrin expression and their ion channel binding partners. This review provides an updated overview of ankyrin proteins and their known channel and transporter interactions. We further discuss several potential avenues of future research that would expand our understanding of these important organizational proteins.

The GluA1-Related BDNF Pathway Is Involved in PTSD-Induced Cognitive Flexibility Deficit in Attentional Set-Shifting Tasks of Rats

Background: Post-Traumatic Stress Disorder (PTSD) is a severe psychological disorder characterized by intrusive thoughts, heightened arousal, avoidance, and flashbacks. Cognitive flexibility dysfunction has been linked with the emergence of PTSD, including response inhibition deficits and impaired attentional switching, which results in difficulties for PTSD patients when disengaging attention from trauma-related stimuli. However, the molecular mechanisms of cognitive flexibility deficits remain unclear. Methods: The animals were exposed to a single prolonged stress and electric foot shock (SPS&S) procedure to induce PTSD-like features. Once the model was established, the changes in cognitive flexibility were assessed using an attentional set-shifting task (ASST) in order to investigate the effects of traumatic stress on cognitive flexibility. Additionally, the molecular alterations of certain proteins (AMPA Receptor 1 (GluA1), brain-derived neurotrophic factor (BDNF), and Postsynaptic density protein 95 (PSD95) in the medial prefrontal cortex (mPFC) were measured using Western blot and immunofluorescence. Results: The SPS&S model exhibited PTSD-like behaviors and induced reversal learning and set-shifting ability deficit in the ASST. These behavioral changes are accompanied by decreased GluA1, BDNF, and PSD95 protein expression in the mPFC. Further analysis showed a correlative relationship between the behavioral and molecular alterations. Conclusions: The SPS&S model induced cognitive flexibility deficits, and the potential underlying mechanism could be mediated by GluA1-related BDNF signaling in the mPFC.

miR-146a and miR-200b alter cognition by targeting NMDA receptor subunits

MicroRNAs fine-tune gene regulation and can be targeted for therapeutic purposes. We investigated the physiological roles of miR-146a and miR-200b that are differentially expressed in neurological disorders such as Alzheimer's disease and schizophrenia, particularly in learning and memory mechanisms. Using bioinformatics tools and luciferase assay, we show interaction of these miRNAs with transcripts of N-methyl-D-aspartate receptor (NMDAR) subunits Grin2A and Grin2B. Overexpression of these miRNAs in primary hippocampal neurons caused downregulation of GluN2B and GluN2A proteins. Stereotactic injections of these miRNAs into rat hippocampus caused cognitive deficits in multiple behavioral tests with decreased protein levels of GluN1, GluN2A, GluN2B, AMPAR subunit GluR1, and Neuregulin 1. In pharmacologically treated rat models [MK-801 treated and methylazoxymethanol acetate (MAM) treated], we found upregulated levels of these miRNAs, implying their involvement in downregulating NMDAR subunits in these models. These results suggest the importance of miR-146a-5p and miR-200b-3p in hippocampus-dependent learning and memory.

Oxytocin signaling is necessary for synaptic maturation of adult-born neurons

Neural circuit plasticity and sensory response dynamics depend on forming new synaptic connections. Despite recent advances toward understanding the consequences of circuit plasticity, the mechanisms driving circuit plasticity are unknown. Adult-born neurons within the olfactory bulb have proven to be a powerful model for studying circuit plasticity, providing a broad and accessible avenue into neuron development, migration, and circuit integration. We and others have shown that efficient adult-born neuron circuit integration hinges on presynaptic activity in the form of diverse signaling peptides. Here, we demonstrate a novel oxytocin-dependent mechanism of adult-born neuron synaptic maturation and circuit integration. We reveal spatial and temporal enrichment of oxytocin receptor expression within adult-born neurons in the murine olfactory bulb, with oxytocin receptor expression peaking during activity-dependent integration. Using viral labeling, confocal microscopy, and cell type-specific RNA-seq, we demonstrate that oxytocin receptor signaling promotes synaptic maturation of newly integrating adult-born neurons by regulating their morphological development and expression of mature synaptic AMPARs and other structural proteins.